Electron affinity vertical, adiabatic

The test set used for most comparisons in the present paper is Database/3 18), which was introduced elsewhere. It consists of 109 atomization energies (AEs), 44 forward and reverse reaction barrier heights (BHs) of 22 reactions, 13 electron affinities (EAs), and 13 ionization potentials (IPs). There are a total of 513 bonds among the 109 molecules used for AEs, where double or triple bonds are only counted as a single bond. Note that all ionization potentials and electron affinities are adiabatic (not vertical), i.e., the geometry is optimized for the ions... 

Figure 2.1 Morse potential energy curves for the neutral and negative-ion states of F2. The vertical electron affinity VEa, adiabatic electron affinity AEa, activation energy for thermal electron attachment E, Err — AEa — VEa, EDEA — Ea(F) — D(FF), and dissociation energy of the anion Ez are shown.

Our implementation computes only vertical ionization energies and electron affinities, but experimental results for the G2 species are adiabatic. To facilitate a direct comparison between the theoretical and experimental results, it is necessary that either the theoretical results be corrected to adiabatic values or that the adiabatic values be related to vertical ones. We have chosen the latter approach and have corrected the experimental results with computational data. 

Transitions between anions and neutral species were also calculated with two procedures. In the first, we calculated the vertical P3 electron affinities of neutral species. The experimental adiabatic electron affinities of the neutral molecules were shifted according to... 

As can be seen, generally all electron affinities predicted by ASCF are negative, indicating a more stable neutral system with respect to the anion. The inclusion of correlation via CCSD(T) and NOF approximates them to the available adiabatic experimental EAs, accordingly with the expected trend. The EAs tend to increase in moving from ACCSD(T) to ANOF and then from ANOF to the experiment. It should be noted that the NH anion is predicted to be unbound by CCSD(T), whereas the positive vertical EA value via NOE corresponds to the bound anionic state. 

From the ET spectra vertical electron affinities are obtained. However, for several reasons it would be interesting to know the adiabatic electron affinities, particularly since there might be a large difference between the vertical and the adiabatic electron affinities in these cycloalkynes. Therefore, electrochemical investigations were carried out to find additional evidence for the increased electron affinity. 

IE,IP) ionisation potential. Compare with adiabatic ionisation energy, vertical ionisation energy, electronegativity, and electron affinity. The energy needed to remove an electron from a gaseous atom or ion. 

Figure 20-3. Electron binding energies for molecule M in anionic state are defined pictorially in a representation of the potential energy surfaces of the neutral molecule (M) and anion radical (M ) with the lowest vibration energy level shown for each. During a vertical process, the geometry remains unchanged but for the adiabatic process structural relaxation occurs. Thus the VDE (vertical detachment energy) and VEA (vertical electron affinity) represent the upper and lower bounds to the adiabatic electron affinity (AEA)...

While adiabatic EAs of U and T are known from experiment to be 0 =b 0.1 eV, the uncertainty in the values for the purines A and G is much greater. A and G clearly have negative adiabatic electron affinities which DFT theory suggests to be ca. —0.35 eV (A) and —0.5 to —0.75 eV (G) with their vertical electron affinities... 

Table 21-2. Relative electronic energies and free energies (AE and AG) calculated with respect to the aHX(AT) or aHX(AT)-SPT anion together with the adiabatic electron affinities (AEAG) and electron vertical detachment energies (VDE) for the anionic HX(AT) complexes predicted at the B3LYP/6-31+G" level. AE and AG in kcal/mol AEAG and VDE in eV...

The adiabatic and vertical ionization potentials for Lis are very similar, both being approximately 3.95 eV. This results because of the similar geometries for the 82 state of LisCCsv) and the Ai state of Li3" (D3h). It must be noted, however, that the vertical ionization process for the removal of an electron from linear Lis to give linear Lis leads to the higher ionization potential, 4.39 eV. If both Csv and forms are present in an experiment, a complicated threshold dependence for the ionization process will be observed (j4). The results for Lis exemplify that the fluxional nature of a small metal cluster may complicate the experimental determination of electron affinities and ionization potentials. 

The electron affinities (EA) of the nucleobases have not been determined experimentally. Calculated values for the vertical and adiabatic EA obtained by scaling experimental and calculated values for other aromatic molecules are summarized in Table 1 [33a]. The vertical values follow the order U>T>C>A>G, with U having the largest (most positive) EA. The calculated adiabatic EA for C is less positive than the values for T or U. Chen and Chen [36] have asserted that the electron affinities of the purines are larger than those of the pyrimidines. However, this claim appears to be based upon questionable reduction potential measurements (see p. 114). The nucleobase anion radicals are estimated to be stabilized by c. 3 eV in aqueous solution. 

We calculate the enthalpy of formation at 0 K as the difference between a H"(PF, g, OK) = -8.55 5.0 kcal mol" (1 ) and the selected value of 1.1 0.5 eV (25.366 kcal mol" ) for the electron affinity (EA) of PF. The value of EA refers to the vertical electron detachment process PF"(g) = PF(g) + e" and is taken from the molecular orbital study of O Hare 2). This value was obtained from Hartree-Fock energies and estimated corrections for correlation effects. The estimated uncertainty in EA is 0.5 eV which should be adequate to cover the possibility that the adiabatic value is lower than the vertical EA. Other theoretical predictions of EA include 2.55 eV ( ) and 1.4 eV (4). 

Sometimes, the donor and acceptor are nearly equal in strength and a b. For the strengths, one must not use the adiabatic ionization potential and (adiabatic) electron affinity (AEa) corresponding to the passage of D with its natural skeleton to D with its natural skeleton or from A with its natural shape to A(—) in its natural shape instead, one must take the so-called vertical values of IP (VIP) and Ea (VEa) corresponding to no change in skeleton. Moreover, one must take VIP and VEa for such deformed... 

The data for F6 indicate a positive vertical and adiabatic electron affinity for the ground state. The presence of a low-lying excited state was observed in other experiments with a vertical electron affinity of —0.4 eV [71]. The higher-energy resonances also result from excited states. These data do not provide direct estimates of the adiabatic electron affinity of a molecule, but have been used to calculate pseudo-two-dimensional Morse potential curves for the molecular anions using data from various sources including the ECD [72]. 

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